Botanical Classification of Plants – Classification of Plants By Different Scientists, Their Merits and Demerits With Plant Classification Chart
Classification of plants is their arrangement into groups having common characteristics. These groups are arranged into a system. Similarly, species of flowering plants are placed in a Genus; similar genera are grouped into Families; families with common features are arranged into Orders; orders into Classes and classes into Divisions.
The Aim of Botanical Classification of Plants
The aim of the classification is to place the plant into a hierarchy of ranks or categories such as species, genera, families, and so on. In addition to expressing’ relationship based on common features, classification serves as a filing and information retrieval system and allows easier reference to organisms comprising the filing system, i.e., it provides an idea about the sequence of evolution of plants from simple to more complex and from more primitive to more advanced types.
The Criteria of the Botanical Classification of Plants
The Criteria of the Classification of plants are the Characters on which the classification is based. The characters of an organism are all the features or attributes (leaf width, stamen number, corolla length, locule number, placentation, etc.) possessed by the organism that maybe compared, measured, counted, describe or otherwise assessed. This means that differences, similarities, and discontinuities between plants and taxa are reflected in their characters. The characters of a taxon are determined by observing or analyzing samples of individuals and recording the observations, or by conducting controlled experiments.
Certain characters which are used in description, delimitation, or identification are called Diagnostic Characters, whereas the characters of constant nature, which are used to “help define a group, are termed as Synthetic Characters. A character may be Qualitative Character when it refers to such things as flower color, odour, leaf shape, etc. Or Quantitative Character when it expresses the features that can be counted or measured such as size, length, breadth, etc.
Characters are important as these:
- Provide information for construction of taxonomic system;
- Supply characters for construction of keys for identification;
- Furnish features useful in the description and delimitation of taxa;
- Enable the scientists to use the predictive value of classification.
Morphological and anatomical characters are used for the purpose of classification.
Units of Botanical Classification of Plants
Following are the units used by plant taxonomies.
The fundamental category forming the base of plant classification is the Species. In taxonomic practice, a group of individual plants that is fundamentally alike is generally treated as species. Ideally, a species should be separated by distinct morphological differences from other species in order to have a practical classification. However, it is sometimes difficult to delimit a species precisely.
A species shows quite a large number of variations within its population. To provide recognition to these variations Infra-Specific Categories, i.e., categories below the rank of species, are used. These are Sub-Species, Variety and Form. The categories of sub-species and variety are applied to populations of species in various stages of differentiation and the category of form is generally used to recognize and describe sporadic variations in single morphological features such as occasional white-flowered plants in a normally purple flowered species.
The species are grouped together into an inclusive group Genus, whose species have more characteristics common with each other than with the species of other genera within the same family. Genera therefore, are aggregates of closely related species. The species together. A genus may consist of one species and is known as Monotypic; or many species may be present in a genus, e.g., Senecio of Compositae contains 2000 to 3000 species.
Genera with common characteristics are grouped together into a more inclusive group, the Family. Both reproductive and vegetative features are used to characterize families. The reproductive characters provide more characters for definitions of families than vegetative characters as these are little affected by environment. The characters usually used to delimit families are: ovary position, kinds of pistils and stamens, carpel number, fruit type, symmetry of flower, leaf arrangement, leaf morphology, and habit.
Next higher category is the Order which includes one or more families. Orders are characterized by an aggregate of characters.
Similarly, the orders are arranged into Classes, the classes into Sub-Divisions, and sub-division into a Division.
Different Types of Systems For Plant Classification
Various system of classification of plants, based upon varying characteristics were proposed by the botanists. These systems of classifications are grouped into following four categories:
Artificial System For Plant Classification
When the plants are classified for the sake of convenience, using some arbitrary or at least easily observable characters, often irrespective of their affinity. The classification is called Artificial and the system of classification is termed as Artificial System. Early systems of classification were mostly artificial, for example, Linnaeus used only one character, the (Cannaceae) which are similar in one respect only. Similarly, unlike plants such as Cacti and Cherries were placed together.
Natural Systems For Kingdom Plantae
By the end of 1700s, most botanists realized that there were Natural Affinities among plants. Also, the theory of evolution by Charles Darwin proposed that present day plants have descended from those existing in ancient past through a series of modifications in response to changing environmental conditions. This also suggest that all plants existing, today are related to each other. Therefore, closely related plants should naturally be grouped together, Such, a system of classification is called Natural System. Such a system helps in identification of plants also. This system superseded artificial systems and most of the Pre-Darwanian systems of classification are natural systems including that of Bentham & Hooker’s system of classification. These systems were based upon morphological and reproductive characters.
Phylogenetic System of Classification of Plants
The systems of classification that try to reflect evolution are said to be Phylogenetic. As the impact of evolutionary theory become apparent, taxonomists started using evolutionary concepts into their classification. However, there was no abrupt departure from previous systems. The taxonomists tried to arrange the natural groups of plants in an evolutionary sequence from simple to the most complex. One of the advantages of phylogenetic system is that it is a rich source of information as the identity of a plant is based upon its affinities and evolutionary relationships. Most of the post-Darwanian systems are phylogenetic including that of Engler and Prantll’s system of classification.
Modern Systems of Botanical Classification of Plants
At present, the classification of plant kindom continues to be modified as new information become available. These systems of classification are called Modern Systems. In these systems, modern information from the fields of paleobotany, biochemistry, anatomy, karyology, etc. have been used in classifying the flowering plants. Electron microscopy also helped in formulation of modern systems. Systems of classification proposed by Robert Thorne (1968), Armen Takhtajan (1980), Arthur Cronquist (1981) and Rolf Dahlgren (1981) are modern systems.
History of Plants and Botany Plants Classification
Theophrastus (Father of Botany)
Theophrastus (372-287 BC), Father of Botany, made a pioneering attempt to place his knowledge of plants on scientific footing. He arranged the plants in several groups. He named and described some 500 plants in his book De Historia Plantarum.
Carolus Linnaeus Classification System
Linnaeus is regarded as a father as a modern taxonomy as classification and nomenclature took root in his time practically. Pre-Linnaeus period is governed by classification system of Greeks which were considered as Herbalists, because they classified the plants on the basis of the habit or according to their economic utility. Major change in the classification of plants took place in the middle of eighteenth century Carl van Linnaeus, a Swedish botanist proposed a system of classification based on characters of stamens. He also used binomial nomenclature in his system. Linnaeus classified the plants into 24 classes starting with Monandria (number of stamen one, e.g., Canna), Diandria, Tri-Tetra, Penta-, Hexa-, Hepta-, Octand-, Ennean-, Deca-, Dodecamdria (stamens 12-19, e.g., Euphorbia) Icosandria (stamens – 20 or more, perigynous, e.g., Cactus). Polygamia (flowers polygamodioecious, e.g., Ficus) and Crytogamia (flowers concealed or absent, e.g., Equisetum). Carolus Linnaeus classification system was artificial and resulted in quite unnatural grouping of plants. Linnaeus himself realized this defect and tried to evolve a natural system but he did not live long enough to complete his work.
Bernard de Jussieu Classification of Plants
Bernard de Jussieu improved upon the Linnaeus system and laid down the foundation of a natural system. His work was published by his nephew Anto Laurent de jussieu. They classified the plants into orders, now families and these orders were grouped into 15 classes. They recognised difference between Monocots and Dicots and separated Cryptogams (acotyledons) from seed plants.
Augustin Pyrame de Condolle Classification of Plants – Ap De Candolle Classification
Augustin Pyrame de Condolle (A.P. de Condolle) improved Jussieu’s system. He was of the view that the morphological characters should be the basis of classification rather the physiological processes. He classified the plants into 213 orders (now families). He started describing all the known species of the plants. His work was completed by his son and grandson.
Robert Brown Classification of Plants – Gymnosperms
Robert brown, distinguished Gymnosperms as naked seeded plants from the Angiosperms in which the seeds are enclosed in a vessel.
Stephen Endlicher, distinguished Gymnosperms as naked seeded plants from the Angiosperms in which the seeds are enclosed in a vessel.
- Thallophytes, containing Algae, Fungi and Lichens.
- Carmophytes, containing mosses, ferns and seed plants.
Bentham and Hooker Classification of Plants
Bentham & Hooker, two botanists, proposed a natural system based on the Condelle’s system. They divided the seed plants into 202 orders (now families) grouped into cohorts (now orders).
At the same time, Wilhelm Hofmeister, with the help of compound microscope discovered the phenomenon of alternation of generation in the lower plants. Darwin’s theory of evolution and discovery of the phenomenon of alternation of generation paved the way for initiation of phylogenetic period in the system of classification.
Wilhelm Eichler Classification of Plants
Wilhelm Eichler first introduced phylogenetic trends in classification. He classified the plants into two major groups:
(i) Cryptogamae: Further divided into three major divisions:
(1) Thallophyta with two classes:
(a) Algae (b) Fungi.
(2) Bryophyta with two classes:
(a) Hepaticeae (b) Musci.
(3) Pteridophyta with three classes:
(a) Equisetineae (b) Lycopodineae and (c) Filicineae.
(ii) Phanerogamae: Further divided into two divisions:
(1) Gymnospermae, and (2) Angiospermae: divided into two classes:
(a) Monocotyleae (b) Dicotyleae; further divided into two sub-classes:
(i) Choripetalae (ii) Sympetalae.
Adolph Engler & Karl Prantll Classification of Plants
Adolph Engler in association with Karl Prantll classified the whole plant kingdom on the basis of phylogenetic relations. This system is an elaboration of Eichler’s system.
Charles Edwin Bessey modified Bentham & Hooker’s system, making it a phylogenetic one, on the basis of certain principles called Bessey’s Dicta. He renamed cohorts as orders and the orders as families.
Persons like John Hutchinson, Alfred Barton Rendle, Oswald Tippo, Arthur J. Eames and I. W. Bailey researched in various fields and their work helped in classification. Presently the classification of plants continues to be modified as new information become available.
Modern systems of classification have been proposed by Robert Thorne (1968), Armen Takhtajan (1980), Arthur Consquist (1981), Rolf Dahlgren (1977, 1980, 1981) has attempted to develop phylogenetic classification based upon evolutionary Principles using newly available informations from the field of embryology, chemistry and anatomy.
Bentham & Hooker’s System of Plant Classification
George Bentham and sir joseph Dalton Hooker presented their system in a three volume work in Latin, entitled Genera Plantarum between 1862 and 1883. The system of classification proposed by Bentham and Hooker is a natural system known as bentham and hooker classification system. It has been retained in British and Indian herberia. Bentham and Hooker’s system of classification is a slight modification of de Condolle’s system and is a non-phylogenetic natural system. The flowering plants are divided mainly on the basis of many constant superficial characters neglecting many floral characters. Hence, many closely related families are kept apart and unrelated families are put together.
All seed plants were classified into 3 classes, 3 sub-classes, 21 series, 25 cohorts and 202 orders. Spermatophytes (seed plants) are divided into Dicotyledons, Gymnosperms and Monocotyledons. The origin of the angiosperms is not established and position of the gymnosperms is anamalous, i.e., in between dicotyledons and monocotyledons. Arboreous and herbaceous habits are not considered as important in the classification of angiosperms. The dicotyledons are placed before monocotyledons and probably dicotyledons are considered to be more primitive than monocotyledons. Monocotyledons are divided into 7 Series beginning with Microspermae and ending in Glumaceae. These series include 34 Natural orders. 5 cohorts and 33 Orders; (c) Monochlamydeae, which is classified into 8 Series, consisting of 33 Natural Orders.
A broad outline of Bentham & Hooker’s system of classification is as follow:
Classification of Plants By Bentham & Hooker – Bentham and Hooker Plant Classification Chart
1. Class: Dicotyledons
A – Sub Class: Polypetalae
Corolla of separate petals.
Series l: Thalamiflorae
Stamens hypogynous and usually many. These series include 6 cohorts and 33 orders.
Series ll: Disciflorae
Hypogynous disc often present. Stamens definite as many as twice the number of petals.
This series include 4 cohorts and 23 orders.
Series lll: Clayciflorae
Sepals united, stamens peri or epigynous. This series include 5 cohorts and 27 orders.
B – Sub Class: Gamopetalae
Corolla of united petals.
Series l: Inferae
Stamens as many as petals and alternating with them; ovary inferior.
This series include 3 cohorts and 9 orders.
Series ll: Heteromerae
Stamens as many as corolla lobes and opposite them, or many; ovary superior or inferior, carpels more than 2, generally isomerous with corolla lobes.
Series lll: Bicarpellatae
Stamens as many as corolla lobes and alternating with the or fewe, ovary mostly bicarpellary and superior.
This series includes 5 cohorts and 27 orders.
C – Sub Class: Monochlamydeae
Perianth 1-2 seriate, mostly sepaloid, minute or absent.
Series l: Curvyembryeae
Seeds mostly with endosperm; embryo curved, lateral or peripheral; ovary mostly one ovuled.
This series include 7 natural orders.
Series ll: Multiovulatae aquaticae
Immersed aquatic herbs; ovary syncarpous, many ovuled.
This series include a single natural order.
Series lll: Multiovulatae terrestris
Terrestrial herbs; ovary syncarpous, many ovules.
This series include 3 natural orders.
Series lV: Microembrayeae
Carpels 1-2 ovuled; ovules with copious emdosperm and minute embryo.
This series include 4 natural orders.
Series V: Daphnales
Ovary monocarpellary, rarely syncarpous and 2-4 ovules; plants woody or herbaceous.
This series include 3 natural orders
Series Vl: Achlamydosporeae
Ovary unilocular, 1-3 ovuled; seeds endospermic, without testa. This series include 3 natural orders.
Series Vll: Unisexuals
Flowers strictly unisexual or polygamous.
This series include 9 natural orders.
Series Vlll: Ordines anomaly
This series include 4 natural orders.
2. Class: Monocotyledons
Series l: Microspermae
Inner perianth petaloid, ovary inferior; seeds minute and many.
This series include 3 natural orders.
Series ll: Epigynae
Inner perianth petaloid, ovary inferior, ovules large and few to many.
This series include 7 natural orders.
Series lll: Corenarieae
Inner perianth petaloid, ovary free.
This series include 8 natural orders.
Series lV: Calycinae
Inner perianth sepaloid, rigid or herbaceous.
This series include 3 natural orders.
Series V: Nudiflorae
Perianth absent or reduced.
This series include 5 natural orders.
Series Vl: Apocarpae
Perianth 1-2 seriate or absent: carpel solitary or gynoecium apocarpous.
This series include 3 natural orders.
Series Vll: Glumaceae
Flowers in dense inflorescence subtended by bracts or glumes: perianth reduced, glumaceous or absent: ovary or locules single ovule.
This series include 5 natural orders.
The division Gymnospermae was placed in between dicotyledons and monocotyledons and is further classified into three orders.
This system has some refinements over that of de Condolle’s namely erection of a new series Disciflorae in their Polypetalae and its incorporation between the Thalamiflorae and Calciflorae, and revision of apetalous taxa. The gymnosperms were treated as the third taxon, collateral with and placed between dicotyledons and monocotyledons. Various genera grouped under “orders” and different orders under “cohort” were based on overall similarities and differences. Certain orders which could not be satisfactorily placed by them in any cohort, were treated anomalous orders (Ordines anomali). This clearly indicates that Bentham & Hooker attempted at a natural classification of seed plants taking into consideration all the data available to them.
Merits and Demerits of Bentham & Hooker’s Plant Classification System
- Though this system is not very natural yet it is very easily workable, and is important from the point of view of its applications.
- This system has been worked out as a result of very careful comparative examination of all known genera of phanerogams.
- This classification makes the basis for the arrangement of plants in Kew herbarium and other important herbaria of common wealth countries.
- In this system, greater emphasis has been given on the contrast between free and united petals e.g., the class dicotyledons is divided into three sub-classes, Polypetalae, Gamopetalae.
- A special feature of this system is the addition of Disciflorae and a curious arrangement of dividing certain groups on the basis of aquatic and terrestrial characters.
- In the class monocotyledons, the stress is being given to the relative position of the ovary and perianth characteristics.
- This establishes no phylogenetic relationship in different taxa of plants.
- The greatest disadvantage is the retention in the group Monochlamydeae a number of orders which show affinities with those in which a biseriate perianth is a rule. The Monochlamydeae is considered aside from
- The position of gymnosperms between dicots and monocots is only for convenience rather than an indicating of affinities.
- This system is based mainly on single and mostly artificial characters, with the result that closely related families are widely separated from each other.
- The position of Orchidaceae and Scitamineae at the beginning of monocots is not satisfactory.
- In monocots, much stress is being given to the relative position of the ovary and perianth characters in determining the affinities that seems unjustified by the comparative study of the orders, e.g., the families Iridaceae and Amaryllidaceae exhibit greater affinities to Liliaceae than to Scitamineae and Bromeliaceae with which they are allied in this system because of common character of epigynae.
- The origin of angiosperms was not established.
Englar & Prantll’s Classification of Plants
Englar along with his associate, Prantll expanded his system and published their work in 23-volume Die Naturilichen Pflazenfamilien between 1887-1915.
This system includes original description of a large number of plants with keys for their identification. Engler believed that simple naked, unisexual flowers were primitive. Such flowers are usually found in Amentifers (Catkin inflorescence plants). According to him these flowers have probably derived from gymnospermous ancestors with unisexual strobilus bearing either micro or megasporophylls. This concept is known as Englerian Concept, regarding the origin of angiospermous flower. The origin of bisexual flower was considered from a cluster of male and female flowers within same inflorescence.
The Englerian school of thought also suggest that the unisexual flowers were wind-pollinated like cones of gymnosperms and that the different groups of angiosperms have been derived from various groups of gymnosperms and pteriophytes suggesting a Polyphyletic Origin. Also in his system, the precedence has been given to monocots over dicots.
Englar & Prantll’s Plant Classification Worksheet
Engler and Prantll classified the plant kingdom into 14 Divisions. The Divisions are:
- Embryophyta Siphonogama: This division includes seed plants.
The Embryophyta Siphonogama was further classified into two Sub-Divisions:
1. Gymnosperm: The gymnopserm includes following groups:
2. Angiospermae: Angiosperms are classified into three classes, the Monocotyledons and the Dicotyledons, together consisting of 303 families.
The Monocotyledons have been considered more primitive than the dicotyledons and therefore, have been placed before them. They are classified into 11 orders and 45 families starting with the unisexual and apetalous Pandanales followed by the aquatic Helobiae, Triuridales, Glumiflorae, Princcps, etc, and ending in highly evolved Microspermae.
The Dicotyledons are classified into two sub-classes:
- Archichlamydeae (Polypetlae)
- Sympetalae (Gamopetlae)
Which were further divided into 44 orders and 258 families.
Archichlamydeae include 33 orders of perianthless as well as polypetalous (lowers, while the Sympetalae includes 11 orders of gamopetalous flowers. The orders Verticellatae, Fagales, Salicales, etc., with perianthless unisexual flowers are placed in the beginning of the dicotyledons, followed by the polypetalous orders such as Centrospermac, Ranales, etc. And ending in the sympetalous orders such as Contortae, Tubiflorae, etc. The Compositae is regarded as highly evolved family. The order Centrospermac, Ranales, etc and ending in the sympetalous orders such as Contortae, Tubiflorae, etc. The Composiate is regarded as highly evolved family. The order Centrospermae is regarded as holding an intermediate position connecting the monocotyledons on one hand and the dicotyledons on the other.
Plant Classification Chart of Engler and Prantll’s Modified System
Engler and Prantll modifies their system and introduce the remodeled plant classification chart as follow:
Plant Kingdom was divided into 14 Divisions and these divisions are:
- Embryophyta Siphonogama
Embryophyta Siphonogama was divided into following two Sub-Divisions.
Gymnospermae: This Sub-division of Gymnospermae includes 7 classes.
Angiospermae: This Sub-division of Gymnospermae includes 2 classes.
1. Monocotyledonae has 14 orders 53 families.
- Helobiae (9)
- Triuridales (1)
- Liliflorae (17)
- Juncales (2)
- Bromeliales (1)
- Commelinales (8)
- Graminales (1)
- Principes (1)
- Synanthae (1)
- Spathiflorae (2)
- Pandanales (3)
- Cyperales (1)
- Scitamineae (5)
- Microspermae (1)
2. Dicotyledonae has 48 orders 291 families. Further classified into two Sub-Classes.
Archichilamydeae (Flowers without perianth, polypetalous) has 37 orders 227 families. Out of which 32 orders are mentioned below:
- Casuarinales (1)
- Juglandales (2)
- Balanopales (1)
- Leitnerales (2)
- Salicales (1)
- Fagales (2)
- Urticales (5)
- Tubiflorae (26)
- Plantanginales (1)
- Balanophorales (1)
- Medusandrales (1)
- Polygonales (1)
- Centrospermae (12+1)
- Cactales (1)
- Magnoliales (22)
- Ranunculales (7)
- Piperales (4)
- Aristolohciales (3)
- Guttiferales (16)
- Sarraceniales (3)
- Papaverales (6)
- Batales (1)
- Rosales (19)
- Hydrostachyales (1)
- Podostemales (1)
- Geraniales (9)
- Rutales (12)
- Sapindales (10)
- Juliniales (1)
- Celastrales (3)
- Rhamnales (3)
- Malvales (7)
Merits & Demerits of Engler and Prantll’s System of Classification
- The merits of Engler and Prantll’s system lies in the broad treatment of the whole plant kingdom and it excellent arrangement of the orders and families in a phylogenetic way.
- The gymnosperms are treated separately in this system.
- This system has resulted from the systematic thoroughness with which Englar and his colleagues applied the system to the flora of the world and thus this system has been accepted in every part of the world.
- The large artificial group of Bentahm and Hooker’s system, the Monochlamydeae has been completely abolished, and its families have been distributed among the related forms with free petals in the large series of Englar’s system,
- The treatment of orchids to be more highly evolved than grasses is satisfactory.
- The Sympetalae of this system corresponds the Gamopetalae of Bentham and Hooker’s system.
- This system obscure, the phylogeny of angiosperms, which according to Engler had a polyphyletic origin from an unknown and hypothetical taxon of extinct gymnosperms.
- The acceptance of the derivation of dichlamydous flowers from, monochlamydous flowers is objectionable.
- In this system, the monocots have been considered to be more primitive than dicots, which does not correspond to the present day knowledge.
- Derivation of bisexual flowers from unisexual flowers and parietal placentation from axile placentation are unsatisfactory.
- A primitive order like Helobiae has been placed between two more advanced orders the – Pandanales and Glumiflorae, which is not satisfactory.
- The position of Amentiferae and Centrospermae at the beginning of dicots before Ranales is not satisfactory.
Armen Takhtajan System of Classification
Takhtajan, a leading Russia plant taxonomist is an international authority on phytogeography, origin and phylogeny of flowering plants. He developed a preliminary Phylogenetic diagram of the orders of higher plants presented in 1942 in a proper on structural types of gynoecium and placentation.
The system is based on Phylogenetic principles was first published in 1954 in Russia language and translated in English in 1958 in the book Origin of Angiospermous Plants. Later he traced the evolution of angiosperms and elaborate his system in De Evolutinder Angiospermen (1959) and proposed a new system in Systema et Phylogenia Magnoliophytorum (1966). Subsequently major revision of his classification were made in 1980, 1987, 1997.
He classified angiosperms up to family level. He believed in the monophyletic origin of angiosperms. They were evolved from the seed ferns Lyginopteridophyta. He divided division Magnoliophyta into two classes. Magnoliopsida (dicots) and Liliopsida (monocots). He considered that Magnoliopsida are primitive and Liliopsida have been derived from Magnoliales under Magnoliopsida. The two classes are divided into two subclasses, superorders, orders and families. He accounted 13,000 genera (10,000 in Magnoliopsida and 3,000 in Liliopsida) and 2,50,000 species (190,000 in Magnoliopsida and 60,000 in Liliopsida).
The outline of classification proposed by Takhtajan is as under.
Takhtajan Classification of Plants Including Specially Gymnosperms – Plant Classification Chart By Armen Takhtajan
Class 1. Magnoliopsida
Sub Class 1. Magnoliidae
Sub Class 2. Nymphaeidae
Sub Class 3. Nelumbonidae
Sub Class 4. Rannunculidae
Sub Class 5. Caryophllidae
Sub Class 6. Hamamelididae
Sub Class 7. Dilleniidae
Sub Class 8. Rosidae
Sub Class 9. Cornidae
Sub Class 10. Asteridae
Sub Class 11. Lamiidae
Class 2. Liliopsida (Monocotyledons)
Sub Class 1. Lamiidae
Sub Class 2. Commelinidae
Sub Class 3. Arecidae
Sub Class 4. Alismatidae
Sub Class 5. Triurididae
Sub Class 6. Aridae
Takhtajan considered that angiosperms arose under environmental stress like drought etc.
Takhtajan Principles For Classification of Plants
- Growth Habit
The study of angiosperm revealed that their evolution began with small, relative weakly branched woody forms. Large trees regarded to be originated from primitive small woody angiosperms. Woody plants are primitive than herbaceous and deciduous woody plants.
Palmate venation is considered to be evolved from pinnate venation. Parallel venation is advanced than the reticulate venation. Alternate leaf arrangements is more primitive.
Stomata with subsidiary cells are advance then lacking subsidiary cells.
- Nodal Structure
The unilacunar nodal structure has been derived from tri-pentalacunar types.
- Woody Anatomy
The evolution of vessels is from vessels with scalariform perforations to vessels with simple perforations.
Cymose inflorescence is primitive, the simple cymose give compound cymose and then evolved racemose.
- Floral Structure
There is a gradual transition from spiral to cyclic arrangement and to the fixation of number of floral parts.
The stamens of earliest angiosperms were leaf-like pinnate microphyllus with marginal situated microsprangia.
- Pollen Grains
The main trend of evolution of dicot pollen is from monocolpate to tricolpate and from tricolpate to triporate.
Apocarpous with large number of ovules is more primitive than syncarpous condition.
Unitegmic ovules arose from bitegmic ovule. Thus unitegmic is primitive than bitegmic ovule. Mesogamic and chalazogamic have evolved from progamic condition.
Anemophily arose from entomophily.
The tetrasporic embryo sac is evolved from primitive monosporic.
Primitive seeds were 5-10 mm long, with abundant endosperms, minute undifferentiated embryo, seed coat with multiple integument is the basic primitive characters.
Many seeded follicles, developed from a multicarpellate, apocarpous gynoecia, is most primitive fruit type.
Merits & Demerits of Takhtajan’s System of Classifying Plants
The Important merits of Takhtajan’s system of classification are as follow:
- It reflects the evolutionary relation better than the older systems.
- It is based on 67 phyletic principles.
- He considered the angiosperms the monophyletic and monocots to have originate from dicots.
- Angiosperms are treated as one division Magnoliophyta.
- The sub class Magnoliidae is considered as the most basic group from other sub class.
- Families are small homogenous units, comprising closely related genera.
- Sub class is not based on single character but on consideration of all known informations.
Despite, that Takhtajan tried to remove deficiencies of his system in 1997, some of the defects are still left, which include:
- The main drawback is derivation of monocot from the sock ancestral to Nymphaeales.
- The narrowing defined taxa have resulted in the unwarranted splitting of related groups.
- The system is although the Phylogenetic but still not helpful for classification up to family level.
- Monocot are placed after dicots recent systems of classification place them between primitive angiosperms and Eudicots.